This invention relates to a fuel supply apparatus of an internal combustion engine, more particularly to a fuel supply apparatus of the type including a venturi carburetor provided with a single air suction passage wherein admixing of atomized fuel and air is effected uniformly.
A venturi carburetor is used widely as a means for producing a mixture of fuel and air. There are two types of venturi carburetors, one of which is provided with a single air suction passage. Another is a two stage dual carburetor which is provided with small and large venturis which function under a partial load condition and a high load condition, respectively.
In a former carburetor provided with the single air suction passage, if the diameter of the venturi is small, the loss due to the suction resistance will increase thereby decreasing the maximum output of the engine, although the engine can supply power that can satisfy full load and partial load at low engine speed. On the other hand, when the diameter of the venturi is increased, although the maximum output increases, not only the torque at low engine speed and full load decreases but also the fuel economy at partial load decreases.
To solve these problems, the latter two stages dual carburetor has been employed including the two suction passages wherein a small diameter venturi is used under partial load conditions, whereas a large diameter venturi is used under high load conditions. Even with such a carburetor, there is a problem in the initial fuel supply characteristic of the fuel flow at a main circuit under low load conditions. More specifically, when the air flow-amount is extremely small, the fuel atomization at the small venturi in the first stage is poor so that it is necessary to provide a slow circuit. However, where such slow circuit is provided, a problem is raised in the operative connection between the slow and main circuits. Furthermore, it is difficult to smoothly transfer from the first stage to the second stage when the second stage begins to operate.
To solve these difficulties a variable stage carburetor has been proposed wherein the air velocity is increased for the purpose of enhancing atomization of the fuel even at low load engine operating conditions. But such a carburetor is disadvantageous in that its construction is complicated, requiring high accuracy and increased expense to manufacture.